1. Field of the Invention
The present invention relates to a control device for a hybrid vehicle having an engine and a motor for outputting driving power, and in particular, the present invention relates to a control device incorporating a control technique which controls a lockup clutch provided to a torque converter during regenerative operation of the motor when the vehicle decelerates.
2. Description of the Related Art
As in a control device for an engine and a motor-generator disclosed in Japanese Unexamined Patent Application, First Publication No. 2000-324608, or as in a control device for a vehicle disclosed in Japanese Unexamined Patent Application, First Publication No. 2001-173768, a control device for a vehicle, e.g., for a hybrid vehicle having not only an internal combustion engine but also an electric motor as the drive source, in which the output power of the internal combustion engine or of the motor is transmitted to a transmission via a torque converter comprising a lockup clutch, which controls not only a mechanical oil pump providing oil pressure to the transmission, the torque converter, or the like, but also controls a motor-driven oil pump, has been known in the art.
In such a control device for a vehicle, the motor-driven oil pump is driven by electrical power supplied from a battery device when the internal combustion engine or the motor for driving the mechanical oil pump is in a stopped state, and the motor-driven oil pump is constructed so as to provide oil pressure to the transmission, the torque converter, or the like, when, for example, the vehicle is going to move.
In a conventional control device for a vehicle as mentioned above, because the motor is disposed at an upstream position with respect to the torque converter, driving power is transmitted to the motor from the wheels of the vehicle via the torque converter when the kinetic energy of the vehicle is restored as regenerated electrical energy by the motor during, for example, deceleration of the vehicle.
In such a regenerative operation of the motor, the lockup clutch of the torque converter is maintained in an engaged state so that the torque loss in the torque converter is restrained, and so that the kinetic energy of the vehicle can be effectively restored.
However, when, for example, the revolution rate of the internal combustion engine is lower than a certain value, the discharging pressure of the mechanical pump is decreased, and because the engaging pressure of the lockup clutch in the engaged state is decreased, the torque transmitted via the lockup clutch may be reduced. As a result, the regenerated energy generated by the motor may also be reduced, or even the regenerative operation of the motor may not be performed.
In consideration of the above circumstances, an object of the present invention is to provide a control device for a hybrid vehicle which enables preventing a decrease in the efficiency of regeneration even when the revolution rate of the internal combustion engine is decreased during deceleration of the vehicle.
In order to solve the above problems and to achieve the above object, the present invention provides a control device for a hybrid vehicle comprising: a transmitting section connecting at least one of an internal combustion engine and a motor to drive wheels via a torque converter having a lockup clutch; a motor-driven pump producing oil pressure for operating the lockup clutch; and a regenerative operation control section which, when the vehicle decelerates, operates the motor-driven oil pump so as to set the lockup clutch in a lockup state, and which also operates the motor so as to generate regenerated energy.
According to the above control device for a hybrid vehicle, when the vehicle decelerates, the regenerative operation control section operates the motor-driven oil pump so as to produce hydraulic pressure for operating the lockup clutch so that torque transmission loss in the torque converter during torque transmission from the drive wheels to the motor is reduced; therefore, the efficiency of regeneration can be improved.
A control device of the present invention may further comprise another oil pump which operates in synchronization with the input revolution rate of the torque converter, and which produces oil pressure for operating the lockup clutch, a determining section determining whether the discharging pressure of the oil pump is equal to or less than a predetermined value, wherein the regenerative operation control section operates the motor-driven oil pump when it is determined by the determining section that the discharging pressure of the oil pump is equal to or less than the predetermined value.
According to the above control device, even when the discharge pressure of the oil pump is decreased due to, for example, decrease in the revolution rate of the internal combustion engine during deceleration of the vehicle, the regenerative operation control section operates the motor-driven oil pump when it is determined by the determining section that the discharging pressure of the oil pump is equal to or less than a predetermined value.
Accordingly, for example, even when it is difficult to operate the lockup clutch using the oil pressure produced by the oil pump, the regenerative operation control section can controllably operate the lockup clutch using the oil pressure produced by the motor-driven oil pump; therefore, the efficiency of regeneration can be improved.
Furthermore, in the control device of the present invention, the determining section may determine whether the discharging pressure of the oil pump is equal to or less than a predetermined value by determining whether the revolution rate of the oil pump is equal to or less than a predetermined revolution rate.
According to the above control device, the determining section makes a determination regarding the discharging pressure of the oil pressure based on the revolution rate of the oil pump, or, for example, based on the input revolution rate of the torque converter. In this case, for example, a revolution rate measuring sensor for the internal combustion engine may be used to measure the input revolution rate of the torque converter; therefore, it is possible to measure the discharging pressure of the oil pump without further providing, for example, an oil pressure sensor.
In addition, the control device of the present invention may further comprise a threshold changing section which changes the predetermined revolution rate in accordance with the temperature of the operation oil for operating the lockup clutch.
According to the above control device, the threshold changing section changes the predetermined revolution rate, which is used as a determination threshold in the determining section, in accordance with the temperature of the operation oil. For example, when the temperature of the operation oil is relatively high, it is determined that the discharging pressure of the oil pump will be decreased, and the predetermined revolution rate is set to a higher value so that the motor-driven oil pump properly operates. On the other hand, when the temperature of the operation oil is relatively low, it is determined that a decrease in the discharging pressure of the oil pump is small, and the predetermined revolution rate is set to a lower value.
Accordingly, the motor-driven oil pump can be effectively operated; therefore, the efficiency of regeneration can be improved even when, for example, vehicle speed is low, or the temperature of the operation oil is high.